1. Field of the Invention
The present invention relates to the field of safety devices for hypodermic needles, and in particular to an automatically positioned protective needle guard for a hypodermic needle.
2. Description of Prior Art
The hypodermic needle is one of the most useful tools in modern medicine, but it is also one of the most dangerous. In the urgent environment of ambulances or hospital emergency rooms, a hypodermic needle may accidentally stick a medical worker or patient. These accidental needle stick injuries are the main cause of occupationally acquired Hepatitis B, HIV, and other infections.
The most dangerous time in using a hypodermic needle is immediately before and after performing an injection, when the tip of the needle is usually exposed. At these times, an accidental drop or mis-handling of the needle by the operator could easily cause an accidental stick if the needle is not protected. Thus, there is a need for a needle guard that prevents the needle from being exposed before, during, and after the needle's use. Additionally, the needle guard should automatically re-position itself over the needle, since the operator will not be able to manually position the needle guard during an accidental drop or slip.
There have been numerous attempts to provide needle guards that perform these functions. Most of them involve an elastic element connected to a cover that encases the needle. For example, U.S. Pat. No. 5,256,152 issued to Marks on Mar. 11, 1992 describes a safety needle having a protective sheath for encasing the needle. The sheath has flexible ribs and a cup having an opening mis-aligned with the needle. A force applied to the cup bows the ribs and aligns the needle with the opening, so that the needle tip may pass through the opening into a patient's body.
This simple solution proposed by Marks has several disadvantages. First, it requires a person to handle the tip of the sheath to expose the needle, possibly leading to accidental punctures of the skin. Second, it provides no locking mechanism for keeping the needle encased once it has been used, so that an accidental stick may still occur when the needle is dropped or mis-handled. Third, the sheath is not strong enough to prevent the needle from jabbing through it.
More complex solutions have tried to address each of these problems. U.S. Pat. No. 5,242,401 issued to Colsky on Oct. 9, 1992 describes a protective needle head assembly. The assembly has a hub portion which attaches to a syringe and a cover portion for covering the needle head. The cover slides on a recessed, W-shaped track to expose the needle during use. After use, a spring automatically pushes the cover back along the track to a position covering the needle. This invention has the advantage of not requiring any extra effort to lock the needle in the exposed and covered positions, but its main disadvantage is that it is complicated to build, requiring precise machining for the track.
Another solution involving a needle cover that is guided on a track is described in U.S. Pat. No. 5,292,314 issued to D'Alessio et al. on Feb. 11, 1993. In this device, the needle cover has change-over slots to enable it to change directions when sliding on the track. A spring forces the cover back to its position protecting the needle after the needle is used. This device also has the advantage of locking the cover in a position that protects the needle. Unfortunately, it also has the disadvantage of requiring the user to manually rotate the cover after injection to initiate the return of the cover to the position in which the needle is protected. This manual step between needle exposure and needle covering does not prevent accidental sticks from occurring when the needle is dropped or mis-handled. This device also requires precise machining of the slots, which adds expense to its construction.
A simpler solution involving a manual locking mechanism is described in U.S. Pat. No. 5,246,428 issued to Falknor on Jul. 30, 1992. This device has a sheath that slides between a first position covering the needle and a second position exposing the needle for use. The sheath includes a latching mechanism which can lock the sheath into either position. A spring mounted within the sheath forces the sheath from its second position exposing the needle to its first position covering the needle after the latching mechanism has been manually released by an operator. This invention also suffers from the problem of requiring a manual step between exposing the needle for use and safely covering the needle after use. It is also difficult to produce a latch small enough to fit a sheath for a hypodermic needle, yet strong enough to resist breaking under pressure.
Another assembly having a spring loaded shield and latching mechanism for the shield is described in U.S. Pat. No. 4,863,435 issued to Sturman et al. on Aug. 24, 1988. In this assembly, the shield also moves between a first position covering the needle and a second position exposing the needle for use. However, the latching mechanism is only able to lock the shield in the second position that exposes the needle. After using the needle, the operator manually unlocks the latching mechanism, and the spring forces the shield back to its needle covering position. This invention suffers from the same disadvantage of requiring the operator to manually unlock the latching mechanism before the shield returns to its needle covering position. Additionally, this device has the disadvantage of not allowing the shield to be locked in a position that covers the needle.
Another device for protecting a needle is described in U.S. Pat. No. 5,336,187 issued to Terry et al. on Jun. 24, 1993. In this device, a syringe has a sleeve with a protective sheath for covering the needle of the syringe. A collapsible bellows is mounted inside the sleeve so that the bellows constantly urges the sheath toward a position that covers the needle. During use of the syringe, the pressure exerted on the sleeve by contact with a patient's body causes the sheath to retract so that the needle may be inserted into the body. As the needle is withdrawn from the body, the collapsed bellows expands, causing the sheath to automatically reposition itself in a protective position over the needle. The main disadvantage of this device is that it lacks a mechanism for locking the sheath in a position that covers the needle, so that an accidental pressure applied to the sleeve would also expose the needle, allowing an accidental stick. Additionally, this device must be attached permanently to the syringe, so that the device is not reusable.
Thus, no existing needle guard combines adequate safety features to prevent an accidental needle stick before, during, and after use of the needle. Additionally, no existing needle guard combines these features in a device that is simple to construct, inexpensive to manufacture, and easy to use.